16 THE DEVELOPMENT OF RAW COTTON 



consisted of only two elementary species when first intro- 

 duced, it would soon be complicated. 



The commercial varieties have usually been derived 

 from single plants, or groups of similar plants, selected 

 Origin of fr m these mixtures. Sometimes they have 

 Commercial been bred from an artificial cross, but the 

 Varieties, difference is slight, unless one of the parents 

 was an entirely fresh introduction to the country of growth, 

 which has seldom been the case. Often they have not 

 been bred down to the pure form before being placed on 

 the market, though externally no marked differences were 

 obvious. In other cases they have been introduced from 

 the beginning in a hopeless state of mixture, such as the 

 Assili cotton of Egypt (Fig. 16, Targets 4 and 8), whereof 

 half the flowers were golden-yellow, half light yellow, 

 and the length and outturn of the lint showed nearly 

 50 per cent, of rogues in the second year of its introduc- 

 tion. There are indications that some varieties, other 

 things being equal, are more susceptible to crossing than 

 their neighbours, so that the rate of deterioration of a 

 variety varies ; but it should now be obvious to the reader 

 that even a very small percentage of impurity in a new 

 variety must ultimately leaven the whole lump. Even 

 if the variety is introduced in an absolutely pure con- 

 dition, it is bound to deteriorate in the end, owing to 

 the admixture of neighbouring varieties, such admixture 

 being brought about by imperfect cleaning of ginAeries 

 and perfection is commercially impossible by resowing 

 with other seed, by self-sown seedlings springing up in 

 the field, or by the shooting of rattoon stumps from an 



